1. Field of the Invention
This invention relates to new and useful improvements in controlled drilling systems, and more particularly to a system of apparatus and method for controlled directional drilling utilizing a down hole motor with orienting and circulating tools and apparatus for orienting a bent sub or bent motor housing in relation to the surveying tool in the drill string to control the direction of the hole being drilled.
2. Brief Description of the Prior Art
Drilling systems wherein a drill bit is operated by a down hole motor, such as positive displacement fluid motors or turbine driven motors are known in the art. In such motors, the drill bit is rotated by a rotor turned by flow of fluid, such as drilling fluid through the motor assembly. These down hole motors and drills are used in many cases for angular drilling of wells by supporting the motor on a bent sub or by using a motor having a bent housing. A surveying tool connected in the drill string above the motor senses and controls the direction of drilling. In such apparatus, it is necessary to locate the bend in the bent sub or the bend in a bent motor housing accurately in relation to the surveying tool to permit accurate control. An accurate orientation of the bent sub or bent motor housing in relation to the surveying tool has been difficult with prior art equipment and such difficulties have been largely overcome by this invention.
In drilling with down hole motors, one major problem encountered is that cuttings and debris sometimes block the bore hole. This has been partially overcome by lifting the entire motor assemble off bottom to allow the motor and bit to spin and to use the drilling fluid to blow out the cuttings and debris. There have been attempts to provide a mechanism to blow out cuttings and debris without lifting the motor and bit off bottom but these have not been effective. Devices which open a valve by lifting the drill string have had the disadvantage that the fluid pressure acting across the motor and bit tends to lock the valve in an open position.
Slim hole drilling is less expensive than conventional drilling because it uses smaller tools, rigs, casing, and mud systems. "Slim hole drilling" as used herein refers to drilling operations in which the hole size is smaller than usual. The slim hole is drilled with less than normal diameter tools, for example, 61/2" bit or less. The tight clearances in smaller casing sizes provides some advantages and some disadvantages. Buckling of the pipe is controlled by hole diameter, drill pipe and tool joint size, and the required pushing force or negative drag. Increasing the tool joint diameter reduces buckling problems, however adequate clearance is needed inside the hole and casing for circulation and pipe movement. Because the pipe is in compression when pushed into the horizontal hole and in tension when pulled out of the hole, it must be appreciably stiffer than pipe used under normal conditions. Finally, there is the effect of rotation and bending on the tool joints and larger diameter elements of the drill string.
Tschirky U.S. Pat. No. 3,879,094 discloses a down hole motor consisting of a positive displacement motor having a bearing assembly on the motor housing which has tungsten carbide radial bearings and a plurality of longitudinally spaced axial thrust bearings.
Tiraspolsky U.S. Pat. No. 3,449,030 discloses a bearing assembly for use in down hole motors which includes a plurality of spaced axial thrust bearings having woven wire annular pads which function to absorb shock.
Garrison U.S. Pat. No. 3,594,106 discloses a down hole motor assembly with longitudinally spaced axial thrust bearings and a spring mechanism for absorbing shock.
Maurer et al U.S. Pat. No. 4,114,704 discloses a turbodrill having means to use the pressure of drilling mud to reverse the application of bearing forces from the lower to the upper thrust bearings.
Maurer et al U.S. Pat. No. 4,665,997 discloses a pressure balanced bearing assembly for down hole motors.